Pole vault crossbar

ABSTRACT

A crossbar for pole vaulting, high jumping and the like of triangular cross section is formed of two strips of synthetic resin, a generally flat base strip and an inverted V-shaped strip, the lower portions of the legs of the inverted V-shaped strip being cemented to the base strip. The crossbar is given a predetermined upward arch or camber to counteract the tendency to sag under its own weight. This may be done by cementing the two parts to each other and clamping them in an arched position while the cement is setting, or by applying a tensile stress lengthwise of the base strip and maintaining such tensile stress with the parts clamped in a straight line relationship while the cement is setting. In the latter case release of the clamping pressure causes the composite crossbar to assume an upwardly cambered form, due to internal tensile-compressive stress equilibrium.

United States Patent Primary Examiner-Richard C Pinkham Assistant ExaminerRichard Dror Attorney-Christel & Bean ABSTRACT: A crossbar for pole vaulting, high jumping and the like of triangular cross section is formed of two strips of synthetic resin, a generally flat base strip and an inverted V- shaped strip, the lower portions of the legs of the inverted V- shaped strip being cemented to the base strip. The crossbar is given a predetermined upward arch or camber to counteract the tendency to sag under its own weight. This may be done by cementing the two parts to each other and clamping them in an arched position while the cement is setting, or by applying a tensile stress lengthwise of the base strip and maintaining such tensile stress with the parts clamped in a straight line relationship while the cement is setting. In the latter case release of the clamping pressure causes the composite crossbar to assume an upwardly cambered form, due to internal tensilecompressive stress equilibrium.

Patented March 30, 1971 3,572,697

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JAMES AJQADPAS BY W 4% ATTORNEYS POLE VAULT CROSSBAR BACKGROUND OF THE INVENTION This invention relates to crossbars such as are used in pole vaulting, high jumping, and the like. Such crossbars are generally of triangular cross section and rest on the supporting uprights with the base down and an angular edge up.

In crossbars used in pole vaulting and high jumping a well known problem exists due to the tendency of the crossbar to sag under its own weight. This sagging tendency is of such magnitude that it is frequently necessary, despite the fact that the uprights which support the ends of the crossbar bear height graduations, to measure the actual vertical distance between the ground and the top of the midpoint of the crossbar in order to obtain a sufficiently accurate reading.

In order to minimize this sagging and the attendant inaccu racy, crossbars of high grade are manufactured from magnesium alloys in the form of hollow triangular extrusions. Such crossbars are quite expensive and are subject to a slight degree of sagging. Furthermore, only slight physical contact with the bar by an athlete will bend a magnesium alloy bar and straightening is impractical and generally not acceptable in competitive use.

SUMMARY OF THE INVENTION In order to overcome the objectionable sagging of crossbars heretofore proposed, and also to avoid the very considerable expense involved in the manufacture of extruded magnesium crossbars, the present invention provides a hollow triangular crossbar of synthetic resin or similar- 'material which is fabricated from two longitudinal components. In general these components may comprise a relatively flat base strip and an upper inverted V-member which is cemented or otherwise attached to the base strip. These two components are attached in such a way as to provide a predetermined upward bow or camber, the degree of this bow or camber being such as to substantially equal the normal sagging tendency of the crossbar. Accordingly, when the ends of the crossbar are resting upon the uprights the normal sagging of the crossbar is substantially equalled by the degree of camber initially provided and the crossbar extends in a true horizontal line.

Since the downward arching tendency of the crossbar is readily counteracted by the built-in upward bowing or camber no particular limitations are imposed in selecting materials for crossbars manufactured according to the present invention.

In one representative form of the crossbar of the present invention the flat base strip and the upper inverted V-strip are cemented together to form the desired triangular cross section while these strips are in an upward arched condition. Thus any subsequent sagging tendency is counterbalanced by the builtin upward arching or camber.

When the parts are cemented to each other in such upwardly arched condition forces tending to straighten the crossbar tend to produce a tensile stress in the lower base strip and a corresponding compressive stress in the upper strip, the force required to overcome these stresses being calculated to balance out as against the normal sagging tendency of the crossbar.

The desired built-in upward arch or camber of crossbars constructed in accordance with the present invention may be produced with the component strips extending in a straight line but with the base strip subjected to stretching forces during the cementing and setting phases whereupon the aforesaid tensile and compressive forces in the composite crossbar will produce the desired upward camber when the stretching forces on the lower base strip are released.

The resilience of the crossbar of the present invention, as contrasted with magnesium alloy crossbars, is such that crossbar will yield resiliently upon body contact and return to initial shape under any but the most extreme stresses.

BRIEF DESCRIPTION OF THE DRAWING FIG. I is a transverse cross-sectional view through one form of the crossbar of the present invention;

FIG. 2 is a fragmentary cross-sectional view of a modified form of crossbar;

FIGS. 3, 4 and 5 are similar views showing further modified cross-sectional forms of crossbars;

FIG. 6 is an elevational view showing somewhat schematically one mode of securing the component strips of the crossbar of the present invention in desired relationship; and

FIG. 7 is a further elevational somewhat schematic view showing another mode of securing the component strips of the crossbar of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the form of crossbar shown in FIG. I an inverted V- shaped strip of synthetic resin or other suitable material is designated I0 and a flat base strip of the same material is designated 11. The two strips 10 and 11 are cemented to each other along the interfaces designated 12 in FIG. I by means of an epoxy resin cement or the like. Any suitable form of synthetic resin material may be employed in manufacturing the strips 10 and II, preferred forms being vinyl, polyethylene, or other synthetic resin having glass fibers embedded therein and also an epoxy resin known as Shell 0828, manufactured by Shell Oil Company. In the case of epoxy resin glass fiber reinforcement is not necessary.

The strips 10 and ll of the embodiment of FIG. 1 are cemented to each other in such way as to produce a predeter' mined upward curvature in the resultant crossbar and, to this end, either of two methods may be employed as illustrated, respectively, in FIGS. 6 and 7.

Referring to FIG. 6, upper strip 10 and lower strip 11, after application of epoxy resin cement to the interfaces 12, are clamped between a pair of curved pressure members 14 and 15 so that when the cement has fully cured, and the crossbar is removed from between the pressure members, the desired upward arching of the resultant crossbar is established.

In order to achieve a predetermined arch or camber in the crossbar it may be required to slightly overform the parts I0 and 11 by means of the pressure members I4 and I5, so that when pressure is released the assembled crossbar will retain the desired degree of curvature to counterbalance the normal sagging tendency. Ideally, after the crossbar is released from between the pressure members lldland I5 and is placed on a flat surface with its base strip down, the weight of the crossbar should cause a downward sagging which brings the crossbar to a straight line horizontal extent so that it will lie flat on such a surface.

FIG. 7 shows another means of achieving the desired upward arching or camber of crossbars constructed in accordance with the present invention. In FIG. 7 the upper inverted V-strip l0 and lower base strip 11 are pressed between pressure members 17 and I8 having flat-pressing surfaces. In this embodiment the lower strip II is gripped at its ends in any desired manner and is subjected to stretching forces as indicated by the arrows in FIG. 7 during the period when the cement is setting. In this way the parts are superstressed to produce the desired upward arching or camber. When the tensile or stretching forces on strip 11 are released, and the assembled crossbar is removed from between the pressure surfaces 17 and 18, lower strip Ill tends to contract and thus produce an upward arching of the crossbar.

The embodiment of FIGS. 2 through 5 are assembled in a manner similar to those just described and differ from the embodiment of FIG. 1 only in the form of the meeting surfaces of the upper and lower strips. In FIG. 2 an upper strip 20 and a lower strip 211 are formed to provide a half-lap joint 22. In the embodiment of FIG. 3 an upper strip 30 and a lower strip 31 are shaped to form a tongue and groove joint 32.

In the embodiment of FIG. 4 an upper strip 40 and a lower strip 41 are formed to provide a dovetail joint 42. In this embodiment the parts will be assembled by relative longitudinal sliding movement, as is also the case in FIG. 5. In FIG. 5 the upper inverted V-shaped member 50 and the lower flat strip member 51 are shaped to form an interlocking tongue and groove joint 52. In the case of the tongue and groove and dovetail joints of H08. 3, 4 and 5, sufficient clearance is provided to accommodate a desired layer of epoxy resin or other suitable cementing material.

lclaim:

l. A crossbar for pole vaulting, high jumping and the like, having a base portion and an inverted V-portion fixed thereto to form a crossbar of triangular cross section, said crossbar being cambered upwardly to a degree sufficient to approximately neutralize the tendency of the crossbar to sag under its own weight whereby the crossbar extends in an approximately straight horizontal line when supported at its ends. 

1. A crossbar for pole vaulting, high jumping and the like, having a base portion and an inverted V-portion fixed thereto to form a crossbar of triangular cross section, said crossbar being cambered upwardly to a degree sufficient to approximately neutralize the tendency of the crossbar to sag under its own weight whereby the crossbar extends in an approximately straight horizontal line when supported at its ends.
 2. A crossbar according to claim 1 wherein the two portions are fixed to each other in a linear tensile-compressive stress equilibrium which establishes said upward camber.
 3. A crossbar according to claim 1 wherein said two portions are formed of synthetic resin.
 4. A crossbar according to claim 2 wherein said two portions are formed of synthetic resin.
 5. A crossbar according to claim 1 wherein said inverted V-portion has an internal channel whereby the composite triangular cross section is hollow. 